This invention relates generally to multi-layer micro-fluidic devices. More specifically, the invention relates to micro-fluid devices with patterned channels that are sealed by a thin film gasket process.
Micro-fluidic devices have several implicated applications in fluid management systems. In particular micro-fluidic devices are being examined for applications in the field of separation technology. For example, micro-fluidic devices may be used in electrophoretic separation systems and capillary separations systems. Micro-fluidic devices also have applications as fluid guides or switches in other managed flow systems.
In general micro-fluidic devices with enclosed and/or sealed channels are fabricated in multi-layer processes, whereby channels are patterned onto a suitable substrate. The channel configuration and the channel dimensions are determined by patterning process that is used. In a subsequent step a capping wafer is secured to the patterned substrate through a bonding process that encloses and seals the patterned channels. Most commonly the patterned substrate is a silicon wafer that is patterned by an etching process. Both the substrate material and the etching process that is used effect the dimensional uniformity, shapes and sizes of the channels produced, while the type of substrates and the channel geometryies effect the fluidic properties.
There are several limitations to the micro-fluidic devices that are described in the prior art. One limitation is that a bonding material must be introduced between patterned wafer and capping wafer in order to secure the wafers and to seal the micro-channels. A second limitation is that micro-fluidic devices described in the prior art are limited in their fluidic properties by the wafer materials used. For example, if the micro-fluidic device is made by etching channels in a silicon wafer, and the channels are enclosed with a capping silicon wafer, the inner channel surfaces are silicon surfaces. Therefore, the fluidic properties of the device are to a large degree determined by the silicon wafer. Silicon is often a preferred wafer material in the fabrication process of micro-fluidic devices, but there are several applications for micro-fluidic devices where the inner channel surfaces of the device used are preferably non-silicon surfaces. Examples where silicon channel surfaces are not perferred include situations where fluid solutions are reactive to the silicon surfaces or where the fluid solutions contain materials that adhere strongly to the silicon surfaces and reduce throughput of the device.
In U.S. Pat. No. 5,443,890, xc3x96hman describes a micro-fluidic device that is fabricated by patterning two sets of channels in a silicon wafer. A second wafer is placed on top of the patterned wafer and a sealing/bonding material is injected into the one set of channels in order to adhere the wafers together and seal the channels. The channel walls are silicon surfaces and, therefore, the chemistries and separations properties of devices produced by this method can only be altered by the dimensions of the channels. Ekstrom et al., in U.S. Pat. No. 5,376,252 describe a micro-fluidic device that is made by laminating a molded spacer layer or layers between two wafers, whereby the spacer layer define the side walls of the channels. Because the spacer layer materials define portions of the enclosed channels the material used for the spacers will effect the fluidic properties of the device. However, substantial portions of the channel surfaces are still dictated by the wafer materials used to laminate the spacer materials. Further, Ekstrxc3x6m et al. do not describe or suggest a method for sealing and securing the wafers together.
What is needed is a method to produce micro-fluidic devices from silicon based materials where the channels of the device have modified channel surfaces tailored to the application at hand. Further, what is need is a method for securing wafers together and sealing the channels in micro-fluidic devices, which does not require the injection of an additional bonding material. The method should provide avenues to produce a variety of devices with different geomerties and with different fluidic properties.
An object of the present invention is to provide a micro-fluidic device that is suitable for use in separations and fluid management systems. The device can be fabricated with channels of various dimensions and a variety of surface properties.
The object of the present invention is accomplished by patterning a substrate with a silicon-based working surface. The substrate is a silicon wafer or any other substrate with a layer of silicon-based material defining the working surface. The working surface of the wafer is etched to define the approximate channel configuration and channel dimensions. It is preferably that the channel walls have sharp dimensional features, which can be accomplished by Deep Reactive Ion Etching processes.
Once the wafer has been patterned with the channels, a gasket layer is conformally deposited across the silicon-based working surface of the substrate and on the channel walls. For example, a layer of silicon carbide or silicon-nitride is deposited by a CVD method. The material used to deposit the gasket layer substantially defines the fluidic properties of the channel walls and the device that is produced. Suitable gasket material include any material that can be conformally deposited over the irregular surfaces of the patterned silicon surface and which will not break down during the anodic bonding process described below. For example, the gasket material can be a fluorinated material, metallic materials, glass material or a polymeric materials deposited by a method suitable for the material
In a subsequent step, a relief gasket is patterned by removing predetermined portions of the gasket layer from the working surface of the substrate while leaving the portions the gasket layer within the channels and along the channel edges. The relief gasket may be patterned by any suitable technique known in the art including using metal and photo-resist masks.
A second substrate is provide with a glass-based working surface and complimentary relief gasket that can be overlaid on the relief gasket described above. The glass working surface must be capable of being anodically bonded to the silicon-based working surface of the patterned substrate. The complimentary relief gasket is made from a variety of materials, but is typically made from the same material as the first relief gasket.
The two wafers are then aligned with the relief gaskets overlaid and the substrates anodically bonded together through their respective working surface. The anodic bonding secures the substrates together with sufficient strength to seal the channels.